It is well known to utilize the conventional electric power wiring in a building for electrically connecting different units of intercommunication systems for electric transmission of conversations. A typical example of such a system can be found in many apartments and condominium complexes in which each room is provided with a remote unit from which it is possible to actuate a master unit door latch releasing mechanism to unlock the door to the complex. Such systems are also usually provided with an intercom arrangement and means for generating an audible signal so that a visitor can alert the resident of a selected apartment room, and such resident, upon hearing the signal, can communicate with the person operating the master unit, and, if desired, can activate the door latch releasing mechanism to permit the visitor to open the door and enter the apartment building. Such a system is described in U.S. Pat. No. 3,978,468 which issued on Aug. 31, 1976 to Bond et al. In the system described in the Bond et al patent, the master unit comprises a digital code selector which operates to generate a remote unit indentification code signal which is transmitted to the remote unit when the visitor calls the particular apartment room. Each remote unit includes a receiver for receiving the conversation transmission signal and the remote unit identification code signal, both of which are transmitted from the master unit to the remote unit over the electrical power wiring of the building.